1. Field of the Invention
The present invention relates to a method of installing an add-on memory or add-on memories in a system having a computer, a microprocessor, etc.
2. Description of the Related Art
Workstations, personal computers, peripheral equipment, such as printers, and other various devices having microprocessors are generally provided with substrates having at least minimum memories which are necessary for satisfactory function.
A prior art substrate of this type is provided with a socket to which add-on memories are mounted, or a connector in which a substrate is inserted, for improving the function, performance, and the like, of these devices, so as to install add-on memories therein in case of necessity.
FIG. 4 is a block diagram of a substrate on which memories are mounted. In the same figure, the substrate has a CPU 1 to which an address decoder 7, a ROM 5 and an I/O port 6 are connected by way of an address bus 9. Likewise, the CPU 1 is connected to mounting portions on which RAM chips can be mounted, namely, to RAM sockets #1 to #n (n is an arbitrary positive integer) which are represented by 2, 3 and 4 in FIG. 4.
Chip select lines which are represented by 10, 11, 12, 13 and 14 in FIG. 4 are connected between the address decoder 7 and the RAM sockets, the ROM 5 and the I/O driver 6, so that each of the latter can be arbitrarily selected by the former. A data bus 8 is connected between the CPU 1 and the RAM sockets 2, 3 and 4, ROM 5 and the I/O driver 6.
FIG. 5 is a block diagram of the address decoder 7. The address decoder 7 has decoder circuits, which are represented by 30, 31 and 32 in the figure, corresponding to the RAM chips to be mounted on the RAM sockets 2, 3 and 4. The decoder circuits in the figure by 30, 31 and 32 in the figure definitely determine the RAM chips mounted on the RAM sockets 2, 3 and 4 based on addresses which are inputted thereto by way of the address bus 9.
However, in the prior art substrate, since the addresses corresponding to the RAM chips to be mounted on the RAM sockets 2, 3 and 4 are definitely determined by the decoders 30, 31 and 32, there is a possibility that the addresses are not continuous in some positions where the add-on RAM chips are mounted in case of adding the same.